This disclosure relates to a load drive circuit that drives a load such as a solenoid by using a switching element.
A background technique of the load drive circuit is disclosed in Japanese Patent Application Publication No. 2013-16959 (Patent Document 1). This load drive circuit detects a load open state, where a load is not connected to an output terminal because of disconnection between the output terminal and the load or any other reason.
As illustrated in FIG. 5, the load drive circuit includes switching element Q1 including a MOSFET, first comparator CP1, second comparator CP2, and clamp circuit 14. First comparator CP1 compares first reference voltage V1 that is lower than the voltage of power supply E inputted to power supply terminal Vcc with output voltage Vout of output terminal OUT. When output voltage Vout is equal to or higher than first reference voltage V1, first comparator CP1 outputs an H level for detection of the load open state.
Second comparator CP2 compares second reference voltage V2 that is lower than the voltage of power supply E and higher than a clamp voltage Vclamp with output voltage Vout of output terminal OUT. When output voltage Vout is equal to or higher than second reference voltage V2, second comparator CP2 outputs an H level for detection of an output-to-supply short circuit state.
When switching element Q1 is off and load 20 is not connected to output terminal OUT, i.e., load 20 is in the load open state, clamp circuit 14 clamps the voltage of output terminal OUT to the clamp voltage Vclamp that is higher than first reference voltage V1 and lower than the voltage of power supply E.
With the above-described configuration, when the load is in the load open state and switching element Q1 is off, output voltage Vout is clamped to the clamp voltage by the clamp circuit.
In the above state, first comparator CP1 can detect the load open state since first reference voltage V1 of first comparator CP1 is set to GND<V1<Vclamp, whereas second comparator CP2 does not detect the output-to-supply short circuit since second reference voltage V2 of second comparator CP2 is set to Vclamp<V2<E.
Meanwhile, in the output-to-supply short circuit state, the voltage of output terminal OUT rises to the voltage of power supply E, even when switching element Q1 is off. In this state, first comparator CP1 detects the current state as the load open state since first reference voltage V1 of first comparator CP1 is set to GND<V1<Vclamp, whereas second comparator CP2 can detect the output-to-supply short circuit state since second reference voltage V2 is set to Vclamp<V2<E.
In addition, when an N-type MOSFET is used as a high-side transistor of switching element Q1 for output, bootstrap circuit BS is added as illustrated in FIG. 5.